1. Field of the Invention
The invention relates to a bearing structure capable of preventing rolling bodies from inwardly falling, especially to a creative design of a unidirectional bearing structure which can be used in a bike's free wheel and typical machine and which has the advantages of a simplified construction and low production costs as well as great enhancement in production efficiency. Furthermore, the bearing structure according to the invention is suitable for fully automatic mass production and thus it has also the effects of saving time in assembling work, minimizing manufacturing costs, and increasing its competitive edges in market.
2. Description of the Prior Art
FIG. 1 shows a conventional unidirectional bearing structure in which a rolling body 1 of either a ball or roller type is to run in a roller race 2 and a roller groove 3 to govern relative motions between an inner ring 5 and an outer ring 6 and carry loads and an elastic element 4 seated in the roller groove 3 will make the rolling body 1 urged solely by a force in a specified direction, resulting in a unidirectional driving effect.
Since a conventional unidirectional bearing structure needs a very smooth roll of rolling bodies between an inner and an outer ring, and the inner and the outer rings are to precisely constrain the motion of elastic elements and rolling bodies, it is not easy for the production of inner and outer rings and the fabrication generally adopts roll forming or forging of steel pipes followed by heat treatment. The manufacture of rollers is even more difficult. In general, this process uses steel wires or round steel bars as raw material. The material must be cut by a stamping machine, forged in a die, burred by a grinder, and then shrunk in a drum to specified roundness and smoothness. The product is finally finished by quenching and fine grinding. Thus, the entire processing procedure is onerous and complicated.
Moreover, a conventional unidirectional bearing structure is not adaptable to a full automatic production procedure. This is because the elastic elements used in a conventional structure are helical springs, which are manufactured by an automatic machine but are easily tangled with each other when piled up due to their spiral coils. This makes these elastic elements unable to be aligned and delivered by a vibrator conveyer. They need to be untangled manually before use. This fact makes a conventional unidirectional bearing structure unqualified for automatic production.
A conventional unidirectional driven sprocket wheel used as a bicycle free wheel having a like construction is shown in FIGS. 2 and 3. The sprocket wheel primarily consists of an annular hollow sprocket wheel body 10 having external sprocket teeth 11 formed on the outer surface thereof and internal zigzag teeth 12 disposed around the interior hollow thereof, every two adjacent zigzag teeth forming a detention groove 13 and arched grooves 14 and 14' being respectively disposed on two sides of these zigzag teeth; a shaft bushing 15 having an enlarged stop flange 151 formed at the bottom thereof, an arched groove 155 abutting against the flange 151, a groove 152 and recesses 153 provided on the outer surface of the bushing for housing a resilient ring and detent plates respectively, and external screw threads 154 formed on the stepped cylindrical surface of the bushing; a disk sleeve 16 having an arched groove (not shown) formed on the inside surface thereof and internal screw threads 161 provided on the interior hollow wall thereof for engaging with the external screw threads 154; and a plurality of steel balls 191 residing in grooves between the sprocket wheel body 10 and the shaft sleeve 15 and between the sprocket wheel body 10 and the disk sleeve 16 to maintain a smooth slide between these components.
Two detent plates 17 and 18 are seated in the recesses 153 and rotatably secured there by a resilient ring 19 housed in the groove 152. When a force acts on the tail 171 of detent plates, the front end of detent plates will lift. The sprocket wheel is assembled by mounting the shaft sleeve 15 on the hollow sprocket wheel body 10 and then combining them by fastening the disk sleeve 16 to the shaft sleeve 15.
Some drawbacks reside in the conventional sprocket wheel structure used in a bicycle free wheel unidirectional drive.
1. Such a structure has the same shortcomings of complexity and high production cost as a conventional unidirectional bearing. Besides, two detent plates 17 and 18 and the resilient ring 19 can not be assembled by automatic equipment and thus it is not feasible to lower production costs by means of automation production. PA1 2. When the external sprocket teeth are driven to rotate in a counterclockwise direction, two detent plates 17 and 18 incessantly slide over zigzag teeth 12 and detention grooves 13. Consequently the detent plates will be urged by the resilient ring 19 to give the zigzag teeth a beating, thus producing loud noises. PA1 3. The amount of parts in such a structure is up to seventy-eight, including at least seventy-two steel balls and at least six structural parts. Thus the construction is intricate and the assembling work is time-consuming. PA1 an annular main body having inner annular portions arranged on the upper and lower end surface thereof, which inner annular portions define therebetween a rib portion that has at least three roller grooves equidistantly and equiangularly spaced and disposed thereon to form through grooves penetrating through the rib portion, which grooves each has a groove bottom of varying depth and has an elastic element seat integrally formed at the end near the deeper side and an opening connected to the interior hollow of the main body, the wall around which opening extends and forms a reduced neck portion at the opening and which opening has a width smaller than the diameter of rolling bodies so as to prevent rolling bodies from dropping out of the grooves; PA1 a plurality of rolling bodies either of a ball or a roller type, each having an appropriate diameter and a smooth surface; PA1 a plurality of elastic elements having an elastic restoring capability when compressed and being made of a curled thin sheet; and PA1 two locating annular plates each having a rim engageable with locating grooves between the end surfaces of the main body and of inner annular portions to secure the locating annular plate on the top of the inner annular portion.
In view of the above-mentioned drawbacks, this invention provides an improved unidirectional bearing structure in which these drawbacks have been eliminated.